Wagstaff (1978) gives complete prime factorizations of Nn and
En for n=20⁢(2)⁢60 and n=8⁢(2)⁢42, respectively. In
Wagstaff (2002) these results are extended to n=60⁢(2)⁢152 and
n=40⁢(2)⁢88, respectively, with further complete and partial factorizations
listed up to n=300 and n=200, respectively.

For information on tables published before 1961 see
Fletcher et al. (1962, v. 1, §4) and
Lebedev and Fedorova (1960, Chapters 11 and 14).